1. Field of the Invention
The present invention is a light emitting diode, a backlight module, and a light tube thereof; especially, the present invention relates to a light emitting diode, a backlight module, and a light tube thereof having different light distributions in horizontal and the vertical view angles.
2. Description of Related Art
Light emitting diodes with quality of small sizes, light weights and a high response rate are widely applied. For example, white LEDs have been used as a light source in backlight modules, lighting systems and optical projectors recently.
In general, the reflection rate is reciprocal to the optical coupling ratio, in other words, the optical coupling ratio is decreasing with the increasing reflection rate. FIG. 2 shows the simulation of the reflection rate and the incident angle of LEDs when the LEDs are applied in the backlight module. As shown in FIG. 2, when the incident angle of LEDs is larger than 60 degree, the reflection rate is highly increased and the optical coupling ratio is reduced; therefore, the optical coupling ratio of white LEDs is 87%.
As shown in FIG. 1, the encapsulating layer of the white LED 11 of the backlight module 10 of LCD is a circular structure so that the white LED 11 provides a condensing light distribution (i.e., Lambertian distribution) which is means that the light intensity is decreased from the center to the edge. Therefore, the center of each white LED 11 has the highest light intensity and the areas between the adjacent white LEDs 11 have lower light intensity. Thus, there is the light distribution with non-uniformity in the backlight module 10 to result in the hotspot problem.
Similarly, the lighting system has darker areas between the adjacent white LEDs 11 due to the Lambertian distribution of LEDs. Thus, the lighting system has spaced lighter and darker areas to cause the uncomfortness of users.
The view angle of the traditional LEDs is about 120 degree and is not suitable for the optical engine of the projector (i.e., the input angle of the optical is about 60 degree). Therefore, the view angle of LEDs has to be adjusted to apply for the projector. However, the adjustment of the view angle results in the depression of light usage rate. In addition, it is necessary to convert the symmetric circle distribution of traditional LEDs into non-symmetric distribution of 16:9 for meeting the requirement of projector (i.e., the projected image is 16:9). An integration tunnel or a micro-lens array is used for convert the light distribution. However, the usage of the integration tunnel or a micro-lens array will result in the light loss and increase the volume of the projector.
Therefore, in the backlight application, the optical coupling rate cannot be improved because of the Lambertian distribution of LEDs. Furthermore, the hotspot problem occurs due to the non-uniformity of the lights. On the other hand, the glare issue and the low optical coupling rate occur in the lighting system. Moreover, the traditional LEDs will cause the low light usage rate in the optical projectors and the solution for the problems further results in another issue, such that the optical path is increased or the size of the projector is increased.
Consequently, with regard to the resolution of defects illustrated hereinbefore, the inventors of the present invention propose a reasonably designed solution of changing the light distribution for effectively eliminating such defects.